The present invention relates to an ink jet head for ejecting ink drops onto paper or the like to thereby perform printing, and an ink jet recording apparatus mounted therewith.
Recently, a very small actuator has been required in ink jet recording apparatus because of high-speed printing and miniaturization of the apparatus due to multiplication of nozzles. Therefore, there is proposed an ink jet recording apparatus using electrostatic power for an actuator (for example, JP-A-6-71882). In this ink jet recording apparatus, the actuator is constituted by parallel plate electrodes, so that there is a feature that the actuator can be miniaturized and a multi-nozzle can be realized.
The summary of an ink jet head driven by this electrostatic actuator will be described with reference to the sectional view of FIG. 21 and the plan view of FIG. 22. The ink jet head in FIGS. 21 and 22 has a lamination structure in which an electrode glass substrate 100, a diaphragm substrate 200 and a nozzle plate 300 are laminated and bonded with each other. Ink 400 supplied to a reservoir 204 from an ink supply port 104 opened in the electrode glass substrate 100 is distributed to a plurality of cavities 203 equally by an orifice 302. Under the lower side of the cavity 203, a transformable diaphragm 201 is formed so as to constitute an electrostatic actuator 50, facing an counter electrode 10 through an insulating film 202 for preventing shortcircuit. A voltage is applied between the diaphragm 201 and the counter electrode 10 with aid of a common electrode (GND) 20, so that all electrostatic force is generated to thereby transform the diaphragm 201 downward. Then, an ink drop 401 is ejected from a nozzle 301 by the pressure due to a spring force of the diaphragm 201 generated when the applied voltage is removed.
However, in a direct driving system in which voltages are applied to individual counter electrodes 10 directly, n wires for the counter electrodes 10 and one wire for the common electrode (GND) 20, that is, (n+1) wires in total from a control circuit are required when n electrostatic actuators (C1 to Cn) 50 are provided, as shown in the circuit diagram of FIG. 23. Therefore, not only the space for the wiring connection portion is increased, but also it is difficult to ensure the reliability. Particularly, the electrostatic capacity of the electrostatic actuators 50 is so small. It is accordingly coupled to the electrostatic capacity of the respective wires from the common electrode (GND) 20 to cause a possible nonuniformity in the electric characteristic of the electrostatic actuators 50. In addition, the number of ICs required for driving actuators corresponds to the number of the actuators. Accordingly, the cost of a driving circuit is increased.
For Such reasons, in order to reduce the space for the wiring connection portion, such a system is proposed that a latch circuit connected to actuators and an integrated circuit for controlling the latch circuit are installed in a head so as to reduce the number of wires. In this system however, the head itself becomes complicated and expensive because of the integrated circuit installed in the head though the reliability of the connection portion can be improved.
It is an object of the present invention to provide an ink jet head, in which
It is an object of the present invention to provide an ink jet head, in which the total number of wires and the total number of driving ICs are reduced so as to reduce the space for the wiring connection portion, and which is low in price and high in practical reliability.
It is another object of the present invention to provide an ink jet head in which printing accuracy is improved in addition to the above-mentioned object.
It is further object of the present invention to provide an ink jet recording apparatus mounted with the above-mentioned ink jet head.
(1) According to the present invention, provided is an ink jet head comprising a plurality of nozzle holes, a plurality of independent ejection chambers communicating with the nozzle holes respectively, diaphragms constituting at least one-side walls of the ejection chambers respectively, counter electrodes opposite to the diaphragms through air gaps respectively, and a control circuit for applying electric pulses between the diaphragms and the electrodes to charge/discharge therebetween to thereby transform the diaphragms to eject ink drops from the nozzle holes, wherein electrostatic actuators constituted by the diaphragms and the counter electrodes respectively are arranged in a matrix electrically.
(2) According to the present invention, in the ink jet head stated in the above paragraph (1), electrodes the potentials of which are controlled individually are formed on the diaphragms respectively.
(3) According to the present invention, in the ink jet head stated in the above paragraph (2), the control circuit scans the potential of either one of the electrodes formed on the diaphragms or the counter electrodes sequentially.
(4) According to the present invention, in the ink jet head stated in the above paragraph (3), the control circuit applies voltages to the counter electrodes with polarity opposite to that of voltages applied to the electrodes formed on the diaphragms respectively.
In the present invention, electrostatic actuators constituted by diaphragms and counter electrodes are arranged in a matrix. By use of the non-linear characteristic of the electrostatic actuators themselves, time sharing driving can be realized. It is therefore possible to reduce the number of wires and the number of driving ICs without using complicated and expensive integrated circuits or the like.
(5) According to the present invention, in the ink jet head stated in the above paragraph (2), (3) or (4), the control circuit periodically inverts the polarity of electrical pulses applied between the electrodes formed on the diaphragm and the counter electrodes respectively.
(6) According to the present invention, in the ink jet head stated in the above paragraph (5), the control circuit inverts the polarity of the electrical pulses applied between the electrodes formed on the diaphragms and the counter electrodes whenever the control circuit scans an electrode to be scanned.
(7) According to the present invention, in the ink jet head stated in the above paragraph (5), the control circuit inverts the polarity of electrical pulses applied between the electrodes formed on the diaphragms and the counter electrodes respectively whenever the control circuit finishes scanning over all of the electrodes to be scanned.
As mentioned above, in the present invention, the direction of charging to the electrostatic actuators is switched between forward and reverse directions alternately. Accordingly, residual charge after ink ejection is erased, so that the relative quantity of displacement between the diaphragms and the electrodes becomes stable at the time of printing. Therefore, high-resolution printing can be realized.
(8) According to the present invention, in the ink jet head stated in any one of the above paragraphs (3) to (7), the control circuit controls electrodes to be scanned respectively so as to allocate ink colors to the electrodes. Accordingly, color printing can be realized with one head.
(9) In addition, an ink jet recording apparatus according to the present invention is mounted with the above-mentioned ink jet head so as to realize an ink jet recording apparatus by which high-quality printing can be realized.